There has been known an automatic following control device for the purpose of reducing a driving operation work of a driver and achieving a safe travel in an express highway or the like. The automatic following control device is structured such as to detect a following distance and a relative speed between an anteceding car and a self car by an object detecting device attached to a front portion of a vehicle, and control each of actuators of a vehicle in such a manner that the following distance coincides with a previously set target following distance.
In the case that the anteceding car is decelerated, the automatic following control device of the self car executes a decelerating control, for example, by a brake, so as to bring the previously set target following distance into line with an actual following distance between the anteceding car and the self car. As an example of a method of executing the brake control, there is a method of generating a brake liquid pressure by utilizing a pump-up function of a brake liquid pressure of an actuator such as a VDC or the like so as to apply a brake. In the brake control mentioned above, a brake control amount target value (a brake liquid pressure, a deceleration, a drive shaft torque or the like) for keeping the following distance is calculated by a following distance control portion, and a brake control is executed by a control device such as the VDC or the like in accordance with the brake control amount target value.
However, since a certain amount of brake fluid is consumed, there is generated a wasted time until the brake control target value is calculated, the brake is actually operated, and the vehicle starts decelerating.
Accordingly, patent document 1 (JP-B2-3427727) discloses a technique for making a wasted time until a brake is actually applied after starting increasing a brake liquid pressure, by increasing the brake liquid pressure to such a degree that a brake pad comes into contact with a brake rotor, before starting the deceleration by actually applying the brake and in the case that there is no possibility that the vehicle is accelerated, that is, in the case that “an actual throttle opening degree and a target throttle opening degree are both equal to or less than a predetermined value”, in a control of a brake booster.
However, in the case of making the wasted time until the brake is actually applied as short as possible, such as the prior art mentioned above, there is a problem that a pulsation sound of the brake fluid is transmitted into a vehicle chamber, thereby obstructing a quietness of the vehicle.
Particularly, at a time of starting the automatic brake control, a deviation between the brake control amount target value from the following distance control portion and the actual brake control amount becomes large. Accordingly, a rapid change of the brake liquid pressure is necessary for bringing the actual brake control amount into line with the brake control amount target value, and the pulsation sound becomes large.
Further, if the brake is operated in a state in which the throttle of the engine is open wide, “accelerating motion” and “decelerating motion” are simultaneously generated, and this is unsatisfactory for safety. Accordingly, it is impossible to increase the brake liquid pressure to such the degree that the brake pad comes into contact with the brake rotor, before fully closing the throttle.
Accordingly, an object of the present invention is to shorten the wasted time with no problem for safety so as to reduce the pulsation sound of the brake liquid pressure, at a time of controlling the brake liquid pressure.